1. Field of the Invention
Embodiments of the invention described herein pertain to the field of agriculture. More particularly, but not by way of limitation, one or more embodiments of the invention enable a system and method for aflatoxin detection.
2. Description of the Related Art
In recent years researchers have identified many chemical compounds as carcinogenic. These include man-made compounds such as asbestos, and pesticides. On the other hand, naturally formed carcinogenic compounds also exist, including mycotoxins.
One prominent member of the mycotoxins family is aflatoxin. Aflatoxin is a product of the mold Aspergillus jlavus. Aflatoxins are highly aggressive toxins that negatively affect mammal's health and causing organ damage, especially in the liver. Aflatoxins include aflatoxin B1, aflatoxin B2, aflatoxin G1, and aflatoxin G2. Aspergi/lusjlavus mold requires a humid environment, and can proliferate in any medium such as fruits, cereals and nuts. The distribution of aflatoxins in agricultural products has a high level of randomness because mold growth is dependent on many variables, including humidity, wind, shade and other factors. The random distribution of aflatoxin in harvested crops is further increased due to multiple handling operations and processes, including partially or fully automated operations and processes.
Almonds, a tree nut, are susceptible to aflatoxin contamination. When the fruit is ripe, almonds are harvested by shaking almond trees with automated machines. Prior to harvest, orchard soil between rows of trees is cleared and vacuumed to eliminate rocks and other debris. Once the almonds have fallen on the cleared ground, they are swept to the center of the aisle and left there for the hull to dry for a period of up to 3 months. When the hull is dried, the almonds are gathered into trucks using large mechanized vacuum machines and transported to the hulling and shelling process plant. At the hulling and shelling process plant, the hull is removed and the shell is cracked and separated from the almond kernel. The almond kernels are then stored in bins, or silos. The storage atmosphere parameters, such as temperature and humidity, are controlled to minimize molding. While in storage, the almonds continue to dry to a final moisture content. The final moisture content is different from crop year to crop year and agricultural area. On average, the moisture content reaches a stable level of between about 3% to about 4.5%.
Human intoxication with aflatoxin is a serious concern in agricultural operations, including nut harvesting of nuts such as brazil nuts, peanuts, pistachios, walnuts, hazelnuts, pecans, cashews, macadamias, almonds and other nuts and produce. Aflatoxin contamination also generates other effects which reduce yield. To quantify costs associated with aflatoxin contamination with regard to process costs, we need to analyze the almond process flow. Highly random distribution of contamination, in conjunction with high health hazard to humans and animals, drove the U.S. Food and Drug Administration (FDA) and the European Food Safety Authority (EFSA) to establish stringent limits on total aflatoxin content. The maximum allowed total aflatoxin content is of 20 ppb (parts per billion) in the US and 110 ppb in the EU.
Previous research attempting to determine the correlation between aflatoxin and other variables in special storage humidity and harvest atmospheric conditions have failed to generate a predictive method or correlation between variables. Thus, addressing aflatoxin contamination necessarily focuses on the detection of aflatoxin in individual almond batches to eliminate contaminated nuts from the process stream.
There are two primary existing methods for aflatoxin detection: liquid chromatography (LC) and UV fluorescence. Liquid chromatography is a destructive laboratory testing method useful for extracting and separating aflatoxins to determine an aflatoxin concentration of the input product. Since laboratory methods of detection require the sample to be ground up and chemically treated, in a sense destroying the product, test validation is limited. Therefore, the usefulness of the method to remove contaminated nuts from a lot is limited. The results of the liquid chromatography method are at best an estimate of contamination levels for the rest of a batch from which the destroyed sample is obtained.
The UV fluorescence method consists of an excitation light in the UV band or blacklight (BL) spectrum. Once exposed to UV or BL radiation, aflatoxins become fluorescent and phosphorescent. The emitted radiation is evaluated to determine the presence of aflatoxins. Previous research shows a maximum excitation for aflatoxin can be achieved when incident light wavelength is between 360 nm and 390 nm. Based on exposure to BL, previous researches have mapped aflatoxin fluorescence below 580 nm. The Cole-Parmer Technical Library states that aflatoxins all have absorption maxima around 360 nm with a molar absorptivity of about 20,000, where the aflatoxin B toxins are named for their blue fluorescence (425 nm) and the G toxins for their green-blue fluorescence (450 nm). (Available at http://www.coleparmer.com/techinfo/techinfo asp?openlist=D,E,C&htmlfile=aflotoxin.htm). Radiation used in the UV fluorescence method for aflatoxin detection is characterized by wavelength and bandwidth. A light source generating a narrow band of incident light has been preferred to eliminate potential interference between detected fluorescence and incident light from the radiation source. One common element to typical systems and methods is the utilization of narrow band excitation UV light (360 to 365 nm bandwidth).
Existing detection equipment, including color sorting equipment, is constructed based on these results. However, this equipment fails to detect and eliminate aflatoxin contaminated almonds to reduce aflatoxin contamination to an acceptable level. Color sorters employ two light sources and two cameras, which individually take a snap shot of each nut face, one nut at a time. U.S. Pat. No. 4,866,283, entitled “Optical Inspection of Food Products,” is directed to aflatoxin detection in peanuts using laser excitation. The method points out that BL cannot be used for aflatoxin detection because incident and emitted lights reside within the same spectral bandwidth domain. However this research points to an excitation wave length of 363 and an aflatoxin Fluorescence with a maximum pick at 575 nm.
U.S. Pat. No. 4,285,698, entitled “Analysis of Aflatoxins in Peanuts by High Pressure Liquid Chromatograph,” is directed to a method for determining the presence and concentration of aflatoxins in peanuts. A process is described for the chemical extraction of aflatoxin from ground peanuts, which is separated into aflatoxin B1, B2, G1 and G2 using high-pressure liquid chromatography. A fluorescence detector with an excitation filter of 365 nm and an emission filter of 425 nm is used to quantify the aflatoxin present.
U.S. Pat. No. 4,535,248, entitled “Method for Detecting Aflatoxin in Almonds,” is directed to a method for the detection of aflatoxin in almonds compatible with an almond sorting machine. The aflatoxin is detected as determined by violet-purple fluorescence in response to UV light with a wavelength from 320-400 nm.
There are several limitations to the state of the art of aflatoxin detection and testing. Aflatoxin fluorescence is limited to surface present contaminant. At the same time, destructive laboratory testing of individual nuts is not feasible. The random distribution of aflatoxin in a lot, which may range in size up to 20 metric tons (approximately 44,000 lbs), makes it difficult for a destructive test to ensure with a 99% accuracy the absence of contaminant. These limitations cause costly results in the commercial production of almonds. For example, a lot of 80,000 lbs. of almonds may pass aflatoxin quality standards for shipping to the EU for an approximate cost of 3,500.00 US Dollars. However, the lot may be sampled and rejected due to the random distribution of contamination. In this scenario, the lot must be shipped back to the USA for re-processing. The entire lot is than re-processed trough color sorters and hand sorting and re-sampled. The re-processed lot may be exported a second time. In this scenario, the shipping cost exceeds 10,000.00 US Dollars.
To overcome the problems and limitations described above there is a need for an improved system and method for aflatoxin detection.